Background. Frequent premature ventricular contractions (PVCs) can cause LV dysfunction or cardiomyopathy (CM), referred to as PVC-cardiomyopathy (PVC-CM). The mechanism responsible this CM is unclear. A PVC?CM canine model was key not only to prove that PVC-CM can be induced in a normal structural heart, but also to identify preliminary cellular and molecular features that may explain the development of LV dysfunction. Until recently an alternative PVC-Cardiomyopathy model has been described in the swine species. This model appears to have similar echocardiographic features to the canine model, although molecular features remain unknown. The main objective of this study is to validate a PVC-CM in a swine model. Hypotheses. Our main hypotheses is that similar to the PVC-CM canine model, the swine model will demonstrate: 1) mild to moderate LV dysfunction, mild mitral regurgitation and diastolic dysfunction in early- coupled PVC, while early PVCs will demonstrate less degree of LV dyssynchrony when compared to late-coupled PVCs (Aim 1); 2) an increase in interleukin and TNF-alpha signaling, while a decrease in mesenchyme development, neuron projection extension and muscle contraction genes (Aim 2); 3) similar changes in the dyad, characterized by decrease in ICaL and down-regulation of Cav1.2, JPH-2, L-type Ca2+ channel misplacement out of the dyad and decrease in BIN1 with impaired Ca2+-induced Ca2+-release (Aim 3); 3); and 4) a minimum chronic exposure of 25% PVC burden is required to develop PVC-CM (Aim 4). Aim 1. Validate the cardiac structural changes in a PVC-CM swine model and impact of post-extrasystolic potentiation and PVC coupling interval in the development of PVC-CM. Aim 2. Confirm Transcriptomic profiling associated with PVC-CM in the swine model. Aim 3. Corroborate the structural and molecular changes including their role on the pathophysiology of PVC- CM and recovery upon PVC cessation in the swine model. Aim 4. Validate PVC burden, baseline echocardiographic, hemodynamic and molecular features that can predict the development of, or resilience to PVC-CM in the swine model despite identical ventricular ectopy. Methods. 56animals will undergo pacemaker implant to reproduce frequent ventricular ectopy (PVCs). They will be randomized to one of 5 groups: 1) late-coupled 50% PVCs (n=13), 2) early-coupled 50% PVCs (n=13), 3) early-coupled PVCs 33% PVCs (n=10), early-coupled 25% PVCs (n=10), or 4) sham (n=10). At the end of a 12- week PVC period, a recovery phase (disabling PVCs) will be allowed in 5 animals of each group exposed to 50% burden and sham group (Fig. 6). Serial cardiac evaluation and biopsies will allow us to assess LV function, transcriptomic profile, dyad structure, Ca2+ transients (EC coupling), changes in JPH-2 and Cav1.2 expression, function and distribution and their mediators at baseline and different time points of PVC-CM in all groups. Significance. This proposal is designed to validate most echocardiographic, hemodynamic, molecular and cellular changes demonstrated in a new PVC-CM Swine model. A new swine PVC-CM model will provide: 1) corroboration of this clinical entity in mammalians, 2) expand our understanding of the mechanism t of PVC- CM as swine has some favorable techniques and procedures, such as viral transfection with AAV-9 to modify cellular and molecular expression, but most importantly 3) minimize the use of a unique and special large species such as the dog. Understanding the mechanism of PVC-CM will help us to identify high-risk patients to develop PVC-CM, but most importantly find future targets to prevent and treat subjects with PVC-CM.